It is known to react the above-mentioned starting materials in alcohols as solvents. The reaction is preferably performed in secondary or tertiary alcohols, where the alcoholate and the alcohols correspond to each other.
For example, European Patent 0 082 339 describes the preparation of cytosine from unsubstituted nitriles in tert.butanol in the presence of potassium tert. butylate. The yield of no more than 62.3% is unsatisfactory. This yield is achievable only with the secondary and tertiary alcohols, but these are relatively expensive. The lower alkanols, ethanol and methanol, together with their alcoholates, produce even smaller yields.
In accordance with West German Patent 34 34 142, the reaction is performed in two stages. First, an alkali metal salt of urea in suspension or preferably as a solid substance is formed. In this first step lower alkanols may optionally also be used. Of disadvantage is the necessity of removing the alcohol as completely as possible in or after the first step, because otherwise the second step does not go to completion. This requires expensive technical procedures and equipment. In the second process step the reaction with nitriles, also in alcohols, takes place; this reaction produces yields of up to 70% only if the first step is performed as indicated above. The disadvantage is the two-step feature of the process, the double use of alcohols and the limitation of the reaction temperature to 90.degree. C. in the first step, because otherwise the alkali metal salt of urea decomposes and the yield drops drastically. The regeneration of the solvent is cost-and labor-intensive, especially because only anhydrous alcohols can be used over again.